1. Field of the Invention
The present invention relates to a method for producing a nitrile. Particularly, it relates to an improved method for producing a nitrile using an alkane as starting material. Nitriles such as acrylonitrile and methacrylonitrile have been industrially produced as important intermediates for the preparation of fibers, synthetic resins, synthetic rubbers and the like.
2. Discussion of Background
As the most popular method for producing such nitriles, a so-called ammoxidation method has been known in which an alkene, such as propylene or isobutene, is catalytically reacted at a high temperature in a gas phase in the presence of the catalyst. On the other hand, recently, an attention has been drawn to a method wherein an inexpensive lower alkane such as propane or isobutane is used as starting materials, and it is catalytically reacted with ammonia and oxygen in a gas phase.
However, the conventional method for producing a nitrile from an alkane starting material is not fully satisfactory as the yield is still low as compared with the alkene starting material. In order to improve the yield of the nitrile, a method of adding a small amount of an organic halide, an inorganic halide or a sulfur compound to the reaction system has been attempted. However, such a method has a problem of corrosion of the reaction apparatus, and each method has a practical problem for industrial application.
According to conventional methods employing a catalyst system, not only the catalytic performance is inadequate but also it is obliged to adopt disadvantageous reaction conditions with respect to the reaction temperature or the reaction gas composition, in many cases. For example, a method for separating and recovering unreacted alkane from the desired nitrile and recycling it to the reactor, is extremely cumbersome and disadvantageous from the viewpoint of the production cost. Further, by conventional techniques, utilization efficiency of ammonia in the reaction is low, and the reaction is conducted by supplying an excess amount of ammonia, in many cases.